Electronic device package

ABSTRACT

An electronic device package comprises a substrate, a die, and a material having a Young&#39;s modulus of between about 0.1 megapascals and about 20 megapascals (at a solder reflow temperature) for attaching the die to the substrate. In one embodiment, the package utilizes a material having a Young&#39;s modulus of between about 0.1 megapascals and about 20 megapascals (at a solder reflow temperature) for attaching the die to the substrate. In an alternate embodiment, the package utilizes a material having a coefficient of thermal expansion α 2  of less than about 400 (four-hundred) ppm (parts per million)/° C. for attaching the die to the substrate. In another alternate embodiment, the package utilizes a rigid material for attaching the die to the substrate.

RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No.09/775,366, filed on Feb. 1, 2001, which is incorporated herein byreference.

FIELD OF THE INVENTION

This invention relates to packaging, and more particularly to packagingelectronic devices.

BACKGROUND OF THE INVENTION

Electronic devices, such as integrated circuit dice, are packaged usinga variety of materials. For example, plastics, ceramics, and glasses areused as substrates and die carriers, while adhesives and polymers areused to attach dice to substrates or other die carriers. Each of thematerials used to package electronic devices has a coefficient ofthermal expansion that defines a rate of expansion for the material asthe temperature of the material changes.

FIG. 1A is a cross-sectional view of a prior art electronic package 101including an adhesive having a low Young's modulus. The electronicpackage 101 includes a substrate 103, one or more solder balls 105, adie 107, a die attach material 109, a molding compound 111, and a board112. In this exemplary package, substrate 103 is fabricated from aceramic, solder balls 105 are fabricated from a conductor, such as alead-tin alloy, die 107 is fabricated from a semiconductor, such assilicon, germanium, or gallium arsenide, die attachment material 109 isfabricated from a compliant material, such as an adhesive having a lowYoung's modulus, molding compound 111 is formed from an epoxide, andboard 112 is fabricated from a glass-epoxide. The bond wires 114electrically couple the die 107 to a bottom surface 116 of the substrate103.

FIG. 1B is a cross-sectional view of an alternative prior art electronicpackage 125 including an adhesive having a low Young's modulus. Theelectronic package 125 includes a substrate 103, one or more solderballs 105, a die 107, a die attachment material 109, a molding compound111, and a board 112. In this exemplary package, substrate 103 isfabricated from a ceramic, solder balls 105 are fabricated from aconductor, such as a lead-tin alloy, die 107 is fabricated from asemiconductor, such as silicon, germanium, or gallium arsenide, dieattachment material 109 is fabricated from a compliant material, such asan adhesive having a low Young's modulus, molding compound 111 is formedfrom an epoxide, and board 112 is fabricated from a glass-epoxide. Thebond wires 114 electrically couple the die 107 to a top surface 127 ofthe substrate 103.

In the manufacture and assembly of electronic device packages, thedevices and packages are often subject to temperature changes. Forexample, during the manufacture of electronic packages 101 and 125(shown in FIGS. 1A and 1B, respectively), after substrate 103 ispositioned on solder balls 105 above board 112, the temperature ofsolder balls 105 is increased, which causes solder balls 105 to flow andform an electrical connection between substrate 103 and board 112. Thetemperature change that causes the reflow of solder balls 105 alsocauses a temperature change in die 107, substrate 103, and dieattachment material 109.

Temperature changes can cause mechanical stresses in packages 101 and125. Thermal mechanical stress is caused in packages 101 and 125 by achange in temperature and a mismatch between the coefficients of thermalexpansion of die 107, substrate 103, and die attachment material 109.Moisture induced stress is caused by the vaporization, at hightemperatures, of moisture retained in substrate 103 or die attachmentmaterial 109. Either thermal mechanical stress or moisture inducedstress can cause mechanical tolerances in package 101 to be exceeded,which results in package failure. Referring to FIGS. 1A and 1B, packagefailures include package cracking, as shown at cracks 118 and 120,delamination of die attachment material, as shown at delamination point122, deformation of die attachment material, as shown at deformationpoint 124, and other failures. These failures can result in a reductionin device reliability and may cause total device failure. U.S. Pat. Nos.5,679,977 and 5,852,326 teach that attaching a die to a substrate usinga material having a low Young's modulus produces fewer package failuresthan attaching a die to a substrate using a material having a highYoung's modulus, and that improved packaging reliability is obtained byselecting a die attachment material having a very low Young's modulus.In electronic package 125 (shown in FIG. 1B) defects, such asdeformation 129, occur in the die attachment material 109, anddeformation 129 of the die attachment material 109 can result indislocation of the die 107 and destruction of the bond wires 114.

Electronic packages, such as electronic package 101 and electronicpackage 125, are tested using a temperature cycle test. In a temperaturecycle test, an electronic package, such as electronic package 101 orelectronic package 125, is repeatedly heated and cooled. In one form ofthe temperature cycle test, electronic packages 101 and 125 arerepeatedly heated and cooled between minus 65 degrees Centigrade and 150degrees Centigrade. Often this cyclic testing results in “cyclic strain”failures. These failures include separation of die attachment material109 from die 103 and substrate 107 and deformation of die attachmentmaterial 109. Electronic packages that fail a “cyclic strain” test alsooften fail prematurely in the field.

For these and other reasons there is a need for the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional view of a prior art electronic packageincluding an adhesive having a low Young's modulus;

FIG. 1B is a cross-sectional view of an alternative prior art electronicpackage including an adhesive having a low Young's modulus;

FIG. 2A is a cross-sectional view of one embodiment of an electronicpackage according to the present invention;

FIG. 2B is a cross-sectional view of one embodiment of an alternativeelectronic package according to the present invention;

FIG. 3 is a graph showing peeling stress and maximum strain versus theYoung's modulus of a material securing a die to a substrate according tothe present invention;

FIG. 4 is a graph showing peeling stress and maximum strain versus thecoefficient of thermal expansion for a material useful in securing a dieto a substrate according to the present invention; and

FIG. 5 is a block diagram of one embodiment of a computer systemincluding a memory array comprising memory dice packaged according tothe present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following detailed description of the preferred embodiments,reference is made to the accompanying drawings which form a part hereof,and in which is shown by way of illustration specific preferredembodiments in which the invention may be practiced. These embodimentsare described in sufficient detail to enable those skilled in the art topractice the invention, and it is to be understood that otherembodiments may be utilized and that logical, mechanical and electricalchanges may be made without departing from the spirit and scope of thepresent inventions. The following detailed description is, therefore,not to be taken in a limiting sense, and the scope of the presentinvention is defined only by the appended claims.

FIG. 2A is cross-sectional view of one embodiment of electronic package201 according to the present invention. Electronic package 201 comprisesa die 203, a substrate 205, one or more solder balls 207 forelectronically coupling substrate 205 to board 208, a die attachmaterial 209, and a molding compound 211.

Electronic package 201 is not limited to packaging a particular type ofelectronic device or system. Electronic package 201 may be used topackage any type of integrated circuit, device, or system including butnot limited to computing circuits, communication circuits, and memorycircuits. Therefore, electronic package 201 may function as anintegrated circuit package, such as a logic circuit package, an analogcircuit package, or a memory circuit package, or as an electronic systempackage, such as a computing system package or a communication systempackage.

Die 203 is typically fabricated from a semiconductor, such as silicon,germanium, or gallium arsenide. In one embodiment of the presentinvention, die 203 comprises one or more processor circuits, such as areduced instruction set processor or a complex instruction setprocessor. In an alternate embodiment, die 203 comprises one or morecommunication circuits, such as a transmitter, receiver, or transceiver.In still another alternate embodiment, die 203 comprises one or morememory circuits or cells, such as dynamic random access memory circuitsor cells, or static random access memory circuits or cells. Each of thecircuits, cells, processors, communication devices or other complexsystems fabricated on die 203 is typically fabricated from passive andactive devices, such as resistors, capacitors, inductors, transistors,and diodes.

Substrate 205 provides a base for mounting die 203. In the presentinvention, substrate 205 is not limited to a particular material or aparticular structure. Substrate 205 may be fabricated from a flexible orinflexible material. Preferably, substrate 205 is fabricated from achemically inert material that has a coefficient of thermal expansionthat is close to the coefficient of thermal expansion of die 203.Exemplary embodiments of substrates suitable for use in connection withthe present invention include single metal layer substrates ormulti-metal layer substrates, such as printed circuit board (PCB)substrates, such as organic, glass fiber reinforced and ceramicsubstrates, and flexible substrates, such as polyimide tape substrates.Other exemplary embodiments of substrates suitable for use in connectionwith the present invention include multilayer substrates, such asmultilayer BT epoxy substrates having signal, power, and ground layers.

Board 208 provides a base for mounting substrate 205. In addition, board208 can provide a base for mounting additional substrates (not shown).Board 208 is not limited to being fabricated from a particular material.Typically, board 208 is fabricated from an inert material that has acoefficient of thermal expansion about equal to the coefficient ofthermal expansion of substrate 205. In one embodiment, board 208 isfabricated from a ceramic. In an alternate embodiment, board 208 isfabricated from a glass-epoxide. In still another embodiment, board 208is fabricated from FR-4. In another alternate embodiment, board 208 isfabricated from polyimide. Board 208 may include any number ofconductive layers separated by a non-conductive material, such as adielectric. In one embodiment, board 208 includes a single conductivelayer formed on a dielectric base, such as a layer comprising copper ora copper alloy formed on FR-4. In an alternate embodiment, board 208includes two or more conductive layers separated by a dielectric, suchas layers comprising metal or metal alloys, such as copper alloysseparated by polyimide.

The one or more solder balls 207 are preferably fabricated from aconductive material. In one embodiment, the conductive material is ametal or metal alloy. Metals and metal alloys used in exemplaryembodiments of the present invention include aluminum, copper, tin,gold, silver, lead, and alloys of aluminum, copper, tin, gold, silver,or lead. Each of the one or more solder balls 207 has a solder reflowtemperature. The solder reflow temperature is the temperature at whicheach of the one or more solder balls 207 makes a sustainable electricalconnection to pads (not shown) on substrate 205 and the electricalconnection sites (not shown) on board 208. A sustainable electricalconnection is a connection for which small stresses and vibrations atthe electrical connection do not interfere electrical conduction at theconnection. In one embodiment of the present invention, the solderreflow temperature is between about 200 degrees Centigrade and 280degrees Centigrade.

Die attach material 209 provides a structure for mechanically securingdie 203 to substrate 205. Preferably, die attach material 209 maintainscontact with die 203 and substrate 205 during and after a solder reflowprocess, which in one embodiment occurs at between about 200 degreesCentigrade and about 280 degrees Centigrade, as described above. Tomaintain contact with die 203, die attach material 209 should not peelaway from the surface of substrate 205 and should not deform during thesolder reflow process. As noted in the background section, U.S. Pat.Nos. 5,679,977 and 5,852,326 teach that a die attach material having alow Young's modulus provides a more reliable structure than a die attachmaterial having a high Young's modulus. According to the presentinvention, a die attach material having a high Young's modulus providesa more reliable structure than a die attach material having a lowYoung's modulus. Preferably, die attach material 209 has a Young'smodulus of between about 0.1 megapascals and 20 megapascals at thesolder reflow temperature of solder balls 207. In one embodiment of thepresent invention, die attach material 209 has a Young's modulus ofbetween about 0.1 megapascals and 20 megapascals at a solder reflowtemperature of between about 200 degrees Centigrade and about 280degrees Centigrade. In an alternate embodiment, die attach material 209has a low coefficient of thermal expansion. For example, in oneembodiment, die attach material 209 has α₂ of less than about 400(four-hundred) ppm (parts per million)/° C. α₂ is defined as coefficientof thermal expansion at temperature above T_(g), the glassy transitiontemperature. In still another alternate embodiment, die attach material209 is a rigid material, which is a material that is deficient or devoidof flexibility or a material that is not compliant. In still anotheralternate embodiment, die attach material 209 is a non-compliantmaterial having a Shore A hardness of more than about 70. In stillanother alternate embodiment, die attach material 209 has a Shore Dhardness of more than about 20. Hardness is measured with an instrumentcalled a Durometer, which pushes a needle-like probe into a specimen tobe tested. The farther the needle penetrates into the specimen the lowerthe Shore reading. The Shore A scale is typically used to measure thehardness of materials such as rubber. The Shore D scale is typicallyused to measure the hardness of materials such as plastics. However,materials having a Shore A measurement of above about 70 begin to have ahardness similar to plastics, which measure on the low end of the ShoreD scale.

Die attach material 209, as used in connection with the presentinvention, is not limited to a particular material. Any material thatexhibits one of the properties described above is suitable for use inconnection with the present invention. For example, any material thathas a Young's modulus between about 0.1 megapascals and 20 megapascals(at a solder reflow temperature), or an α₂ less than about 400(four-hundred) ppm (parts per million)/° C., or that exhibits rigidityis suitable for use in connection with the present invention. Exemplarymaterials that are suitable for use in connection with the presentinvention include epoxides, poly epoxides, acrylates, polyacrylates,polyolefins, and polyimides.

As used herein, an “epoxide” is a cyclic organic compound having anoxygen atom bonded to two other atoms, preferably carbon. As usedherein, an “Epoxy” is a diradical of an epoxide. Suitable epoxides aredisclosed, e.g., in Concise Chemical and Technical Dictionary; 4th Ed.;Chemical Publishing Co., Inc., NY, N.Y. (1986); Aldrich Catalog Handbookof Fine Chemicals, Milwaukee, Wis. (1999); the disclosures of which areincorporated by reference herein.

A specific epoxide of the present invention is a compound of theformula:

wherein

each of R₁, R₂, R₃, and R₄ is independently hydrogen, halo,trifluoromethyl, cyano, hydroxy, nitro, (C₁-C₂₄)alkyl, (C₂-C₂₄)alkenyl,(C₂-C₂₄)alkynyl, (C₃-C₈)cycloalkyl, (C₁-C₂₄)alkyl (C₃-C₈)cycloalkyl,(C₆-C₁₀)aryl, (C₆-C₁₀)heteroaryl, (C₁-C₂₄)alkyl (C₆-C₁₀)aryl,(C₁-C₂₄)alkyl (C₆-C₁₀)heteroaryl, (C₆-C₁₀)aryl (C₁-C₂₄)alkyl,(C₆-C₁₀)heteroaryl (C₁-C₂₄)alkyl, or (C₃-C₈)cycloalkyl (C₁-C₂₄)alkyl;

wherein any alkyl, alkenyl, alkynyl, cycloalkyl, aryl, or heteroaryl canoptionally be substituted with one or more (e.g., 1, 2, 3, or 4) halo,trifluoromethyl, cyano, hydroxy, nitro, C(═O)OR₆, wherein R₆ is hydrogenor (C₁-C₂₄)alkyl, or NR₇R₈, wherein each R₇ and R₈ are independentlyhydrogen or (C₁-C₂₄)alkyl; and

wherein any alkyl, alkenyl, or alkynyl is optionally interrupted withone or more (e.g., 1, 2, 3, or 4) oxo, thio, sulfonyl, or sulfinyl;

or a suitable salt thereof.

In one specific embodiment of the present invention, the epoxide can bea polymer of one or more epoxides (i.e., two ore more epoxy monomers),referred to herein as a poly epoxide. As used herein, a poly epoxide isthe polymerization product of one or more epoxides (i.e., two or moreepoxy monomers). Those of skill in the art know the reaction conditionsin which epoxides can be polymerized. See, e.g., J. March, AdvancedOrganic Chemistry, Reactions, Mechanisms and Structure, (2nd Ed.),McGraw Hill: New York, 1977; F. Carey and R. Sundberg, Advanced OrganicChemistry, Part B: Reactions and Synthesis, (2nd Ed.), Plenum: New York,1977; and references cited therein; which are incorporated by referenceherein. For example, the one or more epoxides can be polymerized underbasic or acidic conditions.

The polymerization of the one or more epoxides can include materials orcompounds that will impart desirable properties to the poly epoxide orthat will catalyze the polymerization process. For example, bisphenol A,bisphenol F, and/or CTBN can be employed in the polymerization process.

The number of epoxy monomers in the poly epoxide can range from 2 toabout 100,000; from 2 to about 25,000; or from 2 to about 10,000.

The poly epoxide can be formed from one or more epoxides (i.e., theepoxy monomers can be the same or different). When the epoxide monomersare different, the resulting poly epoxide will be a copolymer. As usedherein, a “copolymer” is a mixed polymer or heteropolymer formed whentwo or more unlike monomers (e.g., the epoxide monomers) are polymerizedtogether. Concise Chemical and Technical Dictionary; 4th Ed.; ChemicalPublishing Co., Inc., NY, N.Y. (1986), p. 336. In one embodiment of thepresent invention, each of the epoxy monomers are identical. In anotherembodiment of the present invention, all of the epoxy monomers are notidentical (i.e., the epoxy polymer is an epoxy copolymer). In such anembodiment, the number of different epoxy monomers can be from 2 toabout 1,000, from 2 to about 100, or from 2 to about 10.

In one specific embodiment of the present invention, the epoxide can bea mixture of two or more poly epoxides, as defined above. The mixturecan include 2 to about 100 poly epoxides, 2 to about 50 poly epoxides,or 2 to about 10 poly epoxides.

As used herein, a “polyacrylate” is the polymeric material of one ormore esters of alpha beta unsaturated carboxylic acids, e.g., acrylicesters. Suitable acrylic esters include, e.g., methyl acrylate, ethylacrylate, methyl methacrylate, and ethyl methacrylate. Suitablepolyacrylates and acrylic ester monomers are disclosed in, e.g., ConciseChemical and Technical Dictionary; 4th Ed.; Chemical Publishing Co.,Inc., NY, N.Y. (1986); Aldrich Catalog Handbook of Fine Chemicals,Milwaukee, Wis. (1999); the disclosures of which are incorporated byreference herein.

Those of skill in the art know the reaction conditions in whichpolyacrylate can be formed. See, e.g., J. March, Advanced OrganicChemistry, Reactions, Mechanisms and Structure, (2nd Ed.), McGraw Hill:New York, 1977; F. Carey and R. Sundberg, Advanced Organic Chemistry,Part B: Reactions and Synthesis, (2nd Ed.), Plenum: New York, 1977; andreferences cited therein; which are incorporated by reference herein.

Regarding the polyacrylate, the individual esters of the alpha betaunsaturated carboxylic acids can be the same or can be different. In oneembodiment of the present invention, each of the esters of the alphabeta unsaturated carboxylic acids are identical. In another embodimentof the present invention, all of the esters of the alpha betaunsaturated carboxylic acids are not identical (i.e., polyacrylatecopolymer). In such an embodiment (i.e., polyacrylate copolymer), thenumber of different esters of alpha beta unsaturated carboxylic acidscan be from 2 to about 1,000, from 2 to about 100, or from 2 to about10.

As used herein, a “polyimide” is a compound that includes two or moreimide (C(═O)NHC(═O)) linkages. The polyimide can include a sequence of 2to about 100,000 imide linkages, 2 to about 50,000 imide linkages, or 2to about 10,000 imide linkages. The sequence may be linear or cyclic.Suitable polyimides are disclosed, e.g., in Aldrich Catalog Handbook ofFine Chemicals, Milwaukee, Wis. (1999); the disclosure of which isincorporated by reference herein.

Those of skill in the art know the reaction conditions in whichpolyimide can be formed. See, e.g., J. March, Advanced OrganicChemistry, Reactions, Mechanisms and Structure, (2nd Ed.), McGraw Hill:New York, 1977; F. Carey and R. Sundberg, Advanced Organic Chemistry,Part B: Reactions and Synthesis, (2nd Ed.), Plenum: New York, 1977; andreferences cited therein; which are incorporated by reference herein.

A specific polyimide of the present invention is a compound of theformula

wherein

n is 2 to about 1,000;

each R₁, R₂, and R₃ is independently (C₁-C₂₄)alkyl, (C₂-C₂₄)alkenyl,(C₁-C₂₄)alkyl, (C₃-C₈)cycloalkyl, (C₁-C₂₄)alkyl (C₃-C₈)cycloalkyl,(C₆-C₁₀)aryl, (C₆-C₁₀)heteroaryl, (C₁-C₂₄)alkyl (C₆-C₁₀)aryl,(C₁-C₂₄)alkyl (C₆-C₁₀)heteroaryl, (C₆-C₁₀)aryl (C₁-C₂₄)alkyl,(C₆-C₁₀)heteroaryl (C₁-C₂₄)alkyl, or (C₃-C₈)cycloalkyl (C₁-C₂₄)alkyl;

wherein any alkyl, alkenyl, alkynyl, cycloalkyl, aryl, or heteroaryl canoptionally be substituted with one or more (e.g., 1, 2, 3, or 4) halo,trifluoromethyl, cyano, hydroxy, nitro, C(═O)OR₆, wherein R₆ is hydrogenor (C₁-C₂₄)alkyl, or NR₇R₈, wherein each R₇ and R₈ are independentlyhydrogen or (C₁-C₂₄)alkyl; and

wherein any alkyl, alkenyl, or alkynyl is optionally interrupted withone or more (e.g., 1, 2, 3, or 4) oxo, thio, sulfonyl, or sulfinyl;

or a suitable salt thereof.

Regarding the polyimide, the individual imide monomers can be the sameor can be different. In one embodiment of the present invention, each ofthe imide monomers are identical. In another embodiment of the presentinvention, all of the imide monomers are not identical (i.e., polyimidecopolymer). In such an embodiment (i.e., polyimide copolymer), thenumber of different imide monomers can be from 2 to about 1,000, from 2to about 100, or from 2 to about 10.

As used herein, a “polyolefin” is a compound that includes two or moreolefin units (i.e., alkene units). Exemplary olefin units includeethylene, propylene, and butylene. The polyolefin can include 2 to about100,000; 2 to about 50,000; or 2 to about 10,000 olefin units.Additionally, each of the olefin units can be the same or can bedifferent. Specifically, all of the olefin units can be the same.Alternatively, the number of different olefin units can be 2 to about1,000; 2 to about 100; or 2 to about 10.

Those of skill in the art know the reaction conditions in whichpolyolefins can be formed. See, e.g., J. March, Advanced OrganicChemistry, Reactions, Mechanisms and Structure, (2nd Ed.), McGraw Hill:New York, 1977; F. Carey and R. Sundberg, Advanced Organic Chemistry,Part B: Reactions and Synthesis, (2nd Ed.), Plenum: New York, 1977; andreferences cited therein; which are incorporated by reference herein.

Suitable polyolefins are disclosed, e.g., in Aldrich Catalog Handbook ofFine Chemicals, Milwaukee, Wis. (1999); the disclosure of which isincorporated by reference herein.

A specific polyolefin of the present invention is a compound of theformula:

wherein

n is 2 to about 100,000;

each R₁ and R₃ are each independently (C₁-C₂₄)alkyl, (C₂-C₂₄)alkenyl,(C₂-C₂₄)alkyl, (C₃-C₈)cycloalkyl, (C₁-C₂₄)alkyl (C₃-C₈)cycloalkyl,(C₆-C₁₀)aryl, (C₆-C₁₀)heteroaryl, (C₁-C₂₄)alkyl (C₆-C₁₀)aryl,(C₁-C₂₄)alkyl (C₆-C₁₀)heteroaryl, (C₆-C₁₀)aryl (C₁-C₂₄)alkyl,(C₆-C₁₀)heteroaryl (C₁-C₂₄)alkyl, or (C₃-C₈)cycloalkyl (C₁-C₂₄)alkyl;

R₂ is (C₂-C₂₄)alkenyl;

wherein any alkyl, alkenyl, alkynyl, cycloalkyl, aryl, or heteroaryl canoptionally be substituted with one or more (e.g., 1, 2, 3, or 4) halo,trifluoromethyl, cyano, hydroxy, nitro, C(═O)OR₆, wherein R₆ is hydrogenor (C₁-C₂₄)alkyl, or NR₇R₈, wherein R₇ and R₈ are each independentlyhydrogen or (C₁-C₂₄)alkyl; and

wherein any alkyl, alkenyl, or alkynyl of R₁ and R₃ is optionallyinterrupted with one or more (e.g., 1, 2, 3, or 4) oxo, thio, sulfonyl,or sulfinyl;

or a suitable salt thereof.

The material can include an epoxide, a poly epoxide (homopolymer orcopolymer), an acrylic acid, a polyacrylate, an imide, a polyimide, apolyolefin, a mixture thereof, and/or a copolymer thereof. For example,the material can include a mixture of an epoxide, a polyepoxide, anacrylic acid, a polyacrylate, an imide, a polyolefin, and/or apolyimide. Additionally, the material can include a copolymer formedfrom two or more epoxides (i.e., a copolymer), a polymer formed from oneepoxide (i.e., a homopolymer), a polyacrylate, a polyolefin, and/or apolyimide. In one embodiment of the present invention, the material is apoly epoxide. In another embodiment of the present invention, thematerial is a mixture of (1) a poly epoxide and (2) a polyimide. Inanother embodiment of the present invention, the material is a copolymerof (1) a poly epoxide and (2) a polyimide.

FIG. 2B is a cross-sectional view of another embodiment of an electronicpackage 225 according to the present invention. Electronic package 225comprises a die 203, a substrate 205, one or more solder balls 207 forelectronically coupling substrate 205 to board 208, a die attachmaterial 209, and a molding compound 211. Bonding wires 213 electricallycouple a first surface 215 of die 203 to a first surface 217 ofsubstrate 205. Die attach material 209 attaches the die 203 to the firstsurface 217 of substrate 205. The die attach material 209 includesmaterials described above with reference to FIG. 2A. Electronic package225 which includes die attachment material 209 has the same excellentattachment characteristics as electronic package 201 shown in FIG. 2A.Electronic package 225 is less susceptible to cyclic strain, peeling,and cracking, than electronic package 125 (shown in FIG. 1B).

FIG. 3 is a graph 301 showing a simulated peeling stress curve 303 and asimulated maximum strain curve 305 versus the Young's modulus for a dieattach material securing a die to a substrate according to the presentinvention. Peeling stress curve 303 and maximum strain curve 305 weregenerated using finite element analysis. Referring to FIG. 2B peelingstress is the stress at the interface between die attach material 209and substrate 205. In general, the probability of package failureincreases as the peeling stress increases. As can be seen in graph 301,the peeling stress curve 303 decreases rapidly as the Young's modulusincreases from about 1 megapascal to about 4 megapascal. Therefore, theprobability of package failure decreases as the Young's modulusincreases from about 1 megapascal to about 4 megapascal. Again,referring to FIG. 2B, maximum strain is the strain experienced by dieattach material 209. As can be seen in graph 301, the maximum straincurve 305 decreases rapidly as the Young's modulus increases from about1 megapascal to about 4 megapascal. Data shown in graph 301 weregenerated using finite element analysis and can be extrapolated by thoseskilled in the art down to about 0.1 megapascals and out to about 20megapascals (at a solder reflow temperature).

FIG. 4 is a graph 401 showing a simulated peeling stress curve 403 and asimulated maximum strain curve 405 versus a coefficient of thermalexpansion (CTE) for a die attach material securing a die to a substrateaccording to the present invention. Peeling stress curve 403 and maximumstrain curve 405 were generated using finite element analysis. Ingeneral, the probability of package failure increases as the peelingstress increases and as the maximum strain increases. As can be seen ingraph 401, peeling stress curve 403 increases linearly as the CTEincreases from about 100 ppm (parts per million)/° C. to about 500 ppm/°C. Also, as can be seen in graph 401, maximum strain curve 403 increaseslinearly as the CTE increases from about 100 ppm (parts per million)/°C. to about 500 ppm/° C. Therefore, the probability of package failureincreases as the CTE increases from about 100 ppm (parts per million)/°C. to about 500 ppm (parts per million)/° C. Since the probability ofpackage failure increases as the CTE increases, package reliability isincreased by using a die attach material that has a low CTE. In oneembodiment of the present invention, the α₂ for the die attach materialis less than about 400 (four-hundred) ppm (parts per million)/° C.

FIG. 5 is a block diagram of a computer system 500 according to thepresent invention. System 500 comprises processor 505 and memory boardassembly 510. Memory board assembly 510 comprises memory array 515,address circuitry 520, and read circuitry 530, and is coupled toprocessor 505 by address bus 535, data bus 540, and control bus 545. Inone embodiment, the processor 505 is packaged as die 203 in electronicpackage 201, as shown in FIG. 2A. In another embodiment, the memoryarray processor 505 is packaged as die 203 in electronic package 201, asshown in FIG. 2B. In still another embodiment, the memory array 515 ispackaged as die 203 in electronic package 201, as shown in FIG. 2A. Inyet another embodiment, the memory array 515 is packaged as die 203 inelectronic package 225, as shown in FIG. 2B. Processor 505, throughaddress bus 535, data bus 540, and control bus 545 communicates withmemory board assembly 510. In a read operation initiated by processor505, address information, data information, and control information areprovided to memory board assembly 510 through busses 535, 540, and 545.This information is decoded by addressing circuitry 520, including a rowdecoder and a column decoder, and read circuitry 530. Successfulcompletion of the read operation results in information from memoryarray 515 being communicated to processor 505 over data bus 540.

Conclusion

An electronic device package has been described. In one embodiment, theelectronic device package comprises a substrate, a die, and a materialhaving a Young's modulus of between about 0.1 megapascals and about 20megapascals (at a solder reflow temperature) for attaching the die tothe substrate. A package utilizing a material having a Young's modulusof between about 0.1 megapascals and about 20 megapascals (at a solderreflow temperature) shows superior reliability when compared to anintegrated circuit package utilizing a material having a Young's modulusof less than about 0.1 megapascal (at a solder reflow temperature).

The above mentioned problems with electronic device packages and otherproblems are addressed by the present invention and will be understoodby reading and studying the present specification. An electronic devicepackage is described that includes a die attachment material thatreduces peeling stress and strain in an electronic package.

The present invention also provides, in an alternate embodiment, amethod of fabricating an electronic package having high reliability. Themethod comprises mounting a die on a substrate, and securing the die tothe substrate using a die attachment material having a Young's modulusof between about 0.1 megapascals and about 20 megapascals (at a solderreflow temperature) and reflowing the solder balls at a temperature ofbetween about 200 degrees Centigrade and about 280 degrees Centigrade.

These and other embodiments, aspects, advantages, and features of thepresent invention will be set forth in part in the present description,and in part will become apparent to those skilled in the art byreference to the present description and referenced drawings or bypractice of the invention. The aspects, advantages, and features of theinvention are realized and attained by means of the instrumentalities,procedures, and combinations particularly pointed out in the appendedclaims.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement which is calculated to achieve the same purpose maybe substituted for the specific embodiment shown. This application isintended to cover any adaptations or variations of the presentinvention. Therefore, it is intended that this invention be limited onlyby the claims and the equivalents thereof.

1. An electronic system package comprising: a circuit board; a die; anda material having a Young's modulus of between about 0.1 megapascals andabout 20 megapascals at a solder reflow temperature of between about 200degrees Centigrade and 280 degrees Centigrade, the material attachingthe die to the circuit board.
 2. The electronic system package of claim1, wherein the circuit board comprises a flexible circuit board.
 3. Theelectronic system package of claim 1, wherein the die comprises anintegrated circuit fabricated on silicon.
 4. The electronic systempackage of claim 1, wherein the die comprises one or more memorycircuits.
 5. The electronic system package of claim 1, wherein the diecomprises one or more processor circuits.
 6. The electronic systempackage of claim 1, wherein the die comprises one or more logiccircuits.
 7. The electronic system package of claim 1, wherein the diecomprises one or more application specific integrated circuits.
 8. Theelectronic system package of claim 1, wherein the material comprises apoly epoxide formed from one epoxide.
 9. The electronic system packageof claim 1, wherein the material comprises a poly epoxide formed fromtwo or more epoxides.
 10. The electronic system package of claim 1,wherein the material comprises a polyacrylate.
 11. The electronic systempackage of claim 1, wherein the material comprises a polyolefin.
 12. Theelectronic system package of claim 1, wherein the material comprises apolyimide.
 13. The electronic system package of claim 1, wherein thematerial comprises a mixture of at least two of a poly epoxide,polyacrylate, polyimide, and polyolefin.
 14. The electronic systempackage of claim 1, wherein the material comprises a copolymer of atleast two of a poly epoxide, a polyacrylate, polyimide, and polyolefin.15. The electronic system package of claim 1, wherein the materialcomprises a mixture of a poly epoxide and a polyimide.
 16. Theelectronic system package of claim 1, wherein the material comprises acopolymer of a poly epoxide and a polyimide.
 17. The electronic systempackage of claim 1, wherein the material has a Shore A hardness ofgreater than about
 70. 18. The electronic system package of claim 1,wherein the material has a Shore D hardness of greater than about 20.19. An electronic system package, comprising: a circuit board; a die;and a material having a coefficient of thermal expansion a2 of less thanabout 400 (four-hundred) ppm/° C. at a solder reflow temperature ofabout between about 200 degrees Centigrade and about 280 degreesCentigrade, the material attaching the die to the circuit board.
 20. Theelectronic system package of claim 19, wherein the circuit boardcomprises a multi-metal layer circuit board.
 21. The electronic systempackage of claim 19, wherein the die comprises gallium arsenide.
 22. Theelectronic system package of claim 19, wherein the material comprisesone or more polyimides.
 23. The electronic system package of claim 19,wherein the die comprises one or more memory circuits.
 24. Theelectronic system package of claim 19, wherein the die comprises one ormore processor circuits.
 25. The electronic system package of claim 19,wherein the die comprises one or more logic circuits.
 26. The electronicsystem package of claim 19, wherein the die comprises one or moreapplication specific integrated circuits.
 27. The electronic systempackage of claim 19, wherein the material comprises a poly epoxideformed from one epoxide.
 28. The electronic system package of claim 19,wherein the material comprises a poly epoxide formed from two or moreepoxides.
 29. The electronic system package of claim 19, wherein thematerial comprises a polyacrylate.
 30. The electronic system package ofclaim 19, wherein the material comprises a polyolefin.
 31. Theelectronic system package of claim 19, wherein the material comprises apolyimide.
 32. The electronic system package of claim 19, wherein thematerial comprises a mixture of at least two of a poly epoxide,polyacrylate, polyimide, and polyolefin.
 33. The electronic systempackage of claim 19, wherein the material comprises a copolymer of atleast two of a poly epoxide, a polyacrylate, polyimide, and polyolefin.34. The electronic system package of claim 19, wherein the materialcomprises a mixture of a poly epoxide and a polyimide.
 35. Theelectronic system package of claim 19, wherein the material comprises acopolymer of a poly epoxide and a polyimide.
 36. The electronic systempackage of claim 19, wherein the material has a Shore A hardness ofgreater than about
 70. 37. The electronic system package of claim 19,wherein the material has a Shore D hardness of greater than about 20.38. An electronic system package, comprising: a circuit board; a die;and a rigid die attach material attaching the die to the substrate. 39.The electronic system package of claim 38, wherein the circuit boardcomprises a multi-metal layer circuit board.
 40. The electronic systempackage of claim 38, wherein the die comprises germanium.
 41. Theelectronic system package of claim 38, wherein the die comprises one ormore memory circuits.
 42. The electronic system package of claim 38,wherein the die comprises one or more processor circuits.
 43. Theelectronic system package of claim 38, wherein the die comprises one ormore logic circuits.
 44. The electronic system package of claim 38,wherein the die comprises one or more application specific integratedcircuits.
 45. The electronic system package of claim 38, wherein therigid die attach material comprises a poly epoxide formed from oneepoxide.
 46. The electronic system package of claim 38, wherein therigid die attach material comprises a poly epoxide formed from two ormore epoxides.
 47. The electronic system package of claim 38, whereinthe rigid die attach material comprises a polyacrylate.
 48. Theelectronic system package of claim 38, wherein the rigid die attachmaterial comprises a polyolefin.
 49. The electronic system package ofclaim 38, wherein the rigid die attach material comprises a polyimide.50. The electronic system package of claim 38, wherein the rigid dieattach material comprises a mixture of at least two of a poly epoxide,polyacrylate, polyimide, and polyolefin.
 51. The electronic systempackage of claim 3 8, wherein the rigid die attach material comprises acopolymer of at least two of a poly epoxide, a polyacrylate, polyimide,and polyolefin.
 52. The electronic system package of claim 38, whereinthe rigid die attach material comprises a mixture of a poly epoxide anda polyimide.
 53. The electronic system package of claim 38, wherein therigid die attach material comprises a copolymer of a poly epoxide and apolyimide.
 54. The electronic system package of claim 38, wherein therigid die attach material has a Shore A hardness of greater than about70.
 55. The electronic system package of claim 38, wherein the rigid dieattach material has a Shore D hardness of greater than about
 20. 56. Anintegrated circuit package, comprising: a ceramic substrate; a die; anda material having a low coefficient of thermal expansion attaching thedie to the substrate.
 57. The integrated circuit package of claim 56,wherein the ceramic substrate comprises a single layer ceramicsubstrate.
 58. The integrated circuit package of claim 56, wherein thedie comprises a processor fabricated on a semiconductor.
 59. Theintegrated circuit package of claim 56, wherein the die comprises one ormore memory circuits.
 60. The integrated circuit package of claim 56,wherein the die comprises one or more logic circuits.
 61. The integratedcircuit package of claim 56, wherein the die comprises one or moreapplication specific integrated circuits.
 62. The integrated circuitpackage of claim 56, wherein the material comprises one or morepolyolefins.
 63. The integrated circuit package of claim 56, wherein thematerial has a Shore A hardness of greater than about
 70. 64. Theintegrated circuit package of claim 56, wherein the material has a ShoreD hardness of greater than about
 20. 65. The integrated circuit packageof claim 56, wherein the die includes a memory circuit.
 66. Theintegrated circuit package of claim 65, wherein the memory circuitcomprises one or more memory cells.
 67. The integrated circuit packageof claim 65, wherein the die includes a communication system package.68. A method of packaging a die, the method comprising: positioning adie on a substrate; providing a die attach material having a Young'smodulus of between about 0.1 megapascal and 20 megapascals, at a solderreflow temperature, to secure the die to the substrate; and reflowingone or more solder balls in contact with the substrate and a board. 69.A method of packaging a die, the method comprising: positioning a die ona substrate; and providing a die attach material having a coefficient ofthermal expansion of less than about 400 (four-hundred) to secure thedie to the substrate.
 70. An apparatus comprising: a die; a firstsubstrate having a top surface that is attached to a bottom surface ofthe die with a die attach material having a Young's modulus of betweenabout 0.1 megapascals and about 20 megapascals; a second substratehaving a top surface that is attached to the bottom surface of the diewith the die attach material; and a board having a top surface that isattached to a bottom surface of the first substrate with a first set ofone or more solder balls and wherein the top surface of the board isattached to a bottom surface of the second substrate with a second setof one or more solder balls.
 71. The apparatus of claim 70, furthercomprising a molding compound to cover at least part of the firstsubstrate, the second substrate, the die attach material and the die.72. The apparatus of claim 70, wherein the die comprises one or morememory circuits.
 73. The apparatus of claim 70, wherein the diecomprises one or more processor circuits.
 74. The apparatus of claim 70,wherein the die attach material has a Young's modulus of between about 1megapascals and about 4 megapascals.
 75. An apparatus comprising: a die;a substrate having a top surface that is attached to a bottom surface ofthe die with a die attach material having a Young's modulus of betweenabout 0.1 megapascals and about 20 megapascals, wherein the top surfaceof the substrate is electrically coupled to the top surface of the dieusing one or more bonding wires; and a board having a top surface thatis attached to a bottom surface of the substrate with one or more solderballs.
 76. The apparatus of claim 75, further comprising a moldingcompound to cover at least part of the substrate, the die attachmaterial and the die.
 77. The apparatus of claim 75, wherein the diecomprises one or more memory circuits.
 78. The apparatus of claim 75,wherein the die comprises one or more processor circuits.
 79. Theapparatus of claim 75, wherein the die attach material has a Young'smodulus of between about b 1 megapascals and about 4 megapascals.